Comparison of multistranded wire and fiber-reinforced composite retainers effects on periodontium: A randomized clinical trial

ABSTRACT Introduction: Fixed orthodontic retainers are very important for treatment stability; however, adverse effects on the health of periodontium can be caused as a result of deposition of plaque and calculus. Objectives: To compare and determine the effects of two mandibular fixed lingual retainers on the periodontal status, and to test the null hypothesis that there would be no significant difference on the periodontium health between the patients using fiber-reinforced composite (FRC) or multistranded wire (MSW) fixed retainers. Methods: A total of 60 subjects were recruited, out of which 6 were excluded and 2 dropped out during the study. Hence, 52 subjects with mean age of 21.5 ± 3.6 years were included in the study. The sample was composed by 8 males (15.4%) and 44 females (84.6%). The participants were randomly divided into two groups: Group 1 received fiber-reinforced composite retainer, while Group 2 received multistranded wire retainer. After insertion, plaque index, calculus index, gingival index and bleeding on probing were compared, after three months (T1), six months (T2), nine months (T3) and twelve months (T4), using Mann-Whitney test with p-value ≤ 0.05 as significant. Results: It could be seen that the health of periodontium deteriorated with the passage of time from T1 to T4 in both group of retainers. However, no statistically significant differences were found between the two groups (p> 0.05). Conclusion: The results of the study indicate that there was no significant difference on the health of periodontium between the patients with FRC and MSW fixed retainers, hence, the null hypothesis was accepted.

Nagani NI, Ahmed I -Comparison of multistranded wire and fiber-reinforced composite retainers effects on periodontium: A randomized clinical trial

INTRODUCTION
After the completion of the fixed orthodontic treatment, outcome stability is assumed as a great challlenge. 1 It is essential to maintain the teeth on the newly acquired position, thus allowing periodontal and gingival fibers reorganization to prevent relapse. 2 With this regard, orthodontic retainers are bonded at the end of the treatment, being considered a mandatory procedure to several authors. 3 Fixed retainers provide retention for prolonged time, and are the most common choice for the mandibular arch. 4 Multistranded spiral wire retainers (MSW) are flexible in nature and are considered to be the gold standard in providing optimal fixed retention in contemporary orthodontics. 5 Efficacy and reliability of these retainers bonded on the lingual surfaces of anterior teeth have been reported in several studies. 4,5 Fiber-reinforced composites (FRC) are innovative materials with excellent splinting properties, composed of multiple fibers made up of carbon, polyaramid, polyethylene and glass. 6 They are indicated for many applications, such as periodontal splinting, fixed orthodontic retainers, restorations, endodontic post and cores, and bridges. 7,8 FRCs are bonded by chemical adhesion due to the presence of oxygen-inhibited layer on its outer surface, which results in direct chemical bonding with the composite and micromechanical retention of composite resin Nagani NI, Ahmed I -Comparison of multistranded wire and fiber-reinforced composite retainers effects on periodontium: A randomized clinical trial with the tooth surface. 9 FRCs transmit the forces to the glass fibers, thus strengthening the resistance offered by the bonding agent. 10  Thus, the present study tested the null hypothesis that there would be no significant difference in the health of periodontium between the patients with FRC and MSW fixed retainers. In Group 1 subjects, the mandibular anterior dental region was well isolated. Intercanine distance was measured using dental floss, and the correct length of fiber ribbon was cut with a scalpel blade. The ribbon was pretreated with adhesive primer (Transbond™ XT adhesive primer; 3M Unitek). Lingual surfaces of the six anterior teeth were etched with 37% phosphoric acid gel (Meta Biomed) for 30 seconds, washed sufficiently and air-dried. Then, adhesive primer was applied with applicator brush and light-cured with a light emitting diode Eventually, fiber ribbon was conformed to the lingual surfaces of the six anterior teeth with plastic instrument, the excess composite was removed, and each tooth was light-cured for 15 seconds. Further composite resin was applied with applicator for finishing. Finally, each tooth was light-cured for 10 seconds. Oral hygiene instructions were delivered (Fig 2A).
For the Group 2 subjects (multistranded SS retainer), the same isolation and bonding protocols were followed (Fig 2B).
The subjects were called back at every three months interval, for a period of 12 months: three months (T1), six months (T2), nine months (T3) and twelve months (T4). At every visit, the following indices were evaluated on each subject, by the principal investigator and then was reevaluated by two colleagues to avoid errors, and the mean value was recorded.

STATISTICAL ANALYSIS
Shapiro-Wilk test was used to check the normality of the data.
The data was found to be non-normal. Baseline characteristics between the two groups of retainers were investigated using descriptive statistics. P-values were calculated using Independent t-test and Chi-square test. Due to the ordinal data, the four indices were compared and evaluated between two groups of retainers using Mann Whitney test. SPSS v. 21 was used for all data analysis, and the level of significance for all analysis was set to 0.05.

RESULTS
A total of 60 subjects were recruited, out of which 6 were excluded (3 were not meeting the inclusion criteria, while 3 refused to participate). Out of 54 subjects, two dropped out during the study, either because they missed appointment or retainer fracture. Subjects with dislodged or broken retainers had to be excluded to minimize bias, as they were referred immediately for the appliance repair to maintain the stability of the dentition. Hence data was analyzed on 52 subjects (26 in each group) (Fig 1).
The measurement error and reliability between the three observers was checked using intraclass correlation, and good agreement was found between the measurements (ICC > 0.70).  Table 1 shows the comparison of baseline characteristics between the two groups of retainers. There were no significant differences in the baseline characteristics, i.e. age, sex and type of malocclusion, between the two groups.
Nagani NI, Ahmed I -Comparison of multistranded wire and fiber-reinforced composite retainers effects on periodontium: A randomized clinical trial Table 2  showed worse periodontal status than Group 2 (MSW retainers); however, there were no statistically significant differences between the two groups.   Table 2: Comparison of plaque index (PI), calculus index (CI), gingival index (GI) and bleeding on probing (BOP) between two groups of retainers.

DISCUSSION
In this randomized trial, the effects of two frequently used fixed lingual retainers on the periodontium health were determined and compared, using different indices. All cases selected were treated non-extraction in the mandibular arch, to minimize the biasness due to difference in treatment philosophy.
When baseline demographic factors such as age, sex and type of malocclusion were compared, no statistically significant differences were found between the two groups, confirming that these factors did not affect the results of the study. When the results were compared between the two groups of retainers, no significant differences were established between them. When plaque index was compared, plaque deposits were detected in both groups on probing the gingival mar- The present study was performed using a prospective design, allowing to evaluate the results in a reliable manner, as compared to retrospective studies, in which data is insufficient and unpredictable.
Moreover, it was a multicentre study, involving the recruitment of subjects from different areas, thus providing a representative sample.
The limitations included the follow-up time, which was limited to one year (It was not possible to extend the follow-up time of the tria). It was also not possible to blind the observers and the subjects, due to the visible nature of the intervention.
Moreover, the findings of this study are limited to one year post-retention, therefore it could not be predicted whether the plaque and calculus deposits could lead to long-term periodontal problems. Other factors such as level of maintenance of oral hygiene and dietary habits could influence the results.
It is recommended to conduct similar studies with increased sample size and prolonged duration. Periodontal ligament width changes and bone level should also be evaluated in future. It is also suggested to evaluate the effects of other types of fiber-reinforced composites, such as nano-filled composites.

CONCLUSION
The results of the study indicate that there is no significant difference on the health of periodontium between the FRC and MSW fixed retainers, therefore, the null hypothesis was accepted.
Both types of mandibular retainers can be used alternatively.
Mandibular fixed lingual retainers deteriorate the health of periodontium; therefore, routine checkup visits should be planned.